LONDON  Climate change is to blame for alterations in the number and distribution of birds in Britain, and more changes are expected, according to a report published Friday.

Milder winters have pushed bird populations eastward and could result in new bird species being found in Britain, The State of U.K. Birds 2004 report found.

Mark Avery, conservation director for the Royal Society for the Protection of Birds, which helped produce the report, said the impact of climate change was already evident in Britain's bird populations.

"Migratory birds are no respecters of international boundaries and their future is linked to concerted global actions to tackle climate change," Avery said.

Despite a 6 percent rise in the combined populations of 111 bird species since 1970, experts said they were concerned that for every 10 pairs of birds living in rural regions in 1970, fewer than six remained today.

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The report said there had been a rapid decline in species found in farmland environments.

Britain's population of wintering ducks, geese, swans and wading birds had dropped to its lowest level for a decade and seven out of the nine common species of wading birds had shifted from Britain's warm west to the colder east in response to increasingly milder winters there, the report found.

Scientists also predicted that species like the black kite, the cattle egret and the great reed warbler, not currently found in Britain, could migrate there if warmer summer temperatures continued.

The report also highlighted a general trend for birds to nest earlier and for migrating species to arrive earlier than they have done in the past.

"It is now clear that we must adapt the recovery plans for our threatened bird life to take account of the likely effects of climate change on our rural and coastal landscapes," said Phil Grice of the English Nature group, which contributed to the report.